analytics/math3/src/main/java/org/apache/edgent/analytics/math3/stat/Statistic2.java

/*
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regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
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  http://www.apache.org/licenses/LICENSE-2.0

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*/
package org.apache.edgent.analytics.math3.stat;

import org.apache.commons.math3.stat.descriptive.StorelessUnivariateStatistic;
import org.apache.commons.math3.stat.descriptive.moment.Mean;
import org.apache.commons.math3.stat.descriptive.moment.StandardDeviation;
import org.apache.commons.math3.stat.descriptive.rank.Max;
import org.apache.commons.math3.stat.descriptive.rank.Min;
import org.apache.commons.math3.stat.descriptive.summary.Sum;
import org.apache.edgent.analytics.math3.Aggregations;
import org.apache.edgent.analytics.math3.UnivariateAggregate;
import org.apache.edgent.analytics.math3.UnivariateAggregator;

/**
 * Statistic implementations.
 * 
 * Univariate statistic aggregate calculations against a value
 * extracted from a tuple.
 * 
 * Unfortunately the implicitly-Json Statistic wasn't named JsonStatistic.
 * 
 * @see Aggregations
 */
public enum Statistic2 implements UnivariateAggregate {
    
    /**
     * Calculate the number of elements in the collection.
     * The value is represented as a {@code double}
     * with the key {@code COUNT} in the aggregate result.
     */
    COUNT(new Count()),
    /**
     * Calculate the arithmetic mean.
     * The mean value is represented as a {@code double}
     * with the key {@code MEAN} in the aggregate result.
     */
    MEAN(new Mean()),
    /**
     * Calculate the minimum.
     * The minimum value is represented as a {@code double}
     * with the key {@code MIN} in the aggregate result.
     */
    MIN(new Min()),
    /**
     * Calculate the maximum.
     * The maximum value is represented as a {@code double}
     * with the key {@code MAXIMUM} in the aggregate result.
     */
    MAX(new Max()),
    /**
     * Calculate the sum.
     * The sum is represented as a {@code double}
     * with the key {@code SUM} in the aggregate result.
     */
    SUM(new Sum()),
    /**
     * Calculate the standard deviation.
     */
    STDDEV(new StandardDeviation());

    private final StorelessUnivariateStatistic statImpl;

    private Statistic2(StorelessUnivariateStatistic statImpl) {
        this.statImpl = statImpl;
        statImpl.clear();
    }

    /**
     * Return a new instance of this statistic implementation.
     * N.B. must call clear(n) before using the result.
     * @return A new instance of this statistic implementation.
     */
    @Override
    public UnivariateAggregator get() {
        return new StorelessStatistic(this, statImpl.copy());
    }
}